Is learning from a textbook useless?

One of the things ive always heard the most is how polite Japanese culture is. But recently ive been seeing a lot more posts and videos on the internet saying that learning from a textbook wont work because no one actually speaks that way. And that you wont understand anyone and they wont really understand you. So basically am I wasting my time? How do I learn how to be polite but not too polite and not too casual either? Will I really not be able to understand anyone